The present invention relates to a needle for applying viscous fluid such as cream-like solder, and more particularly to a needle which is not clogged with the solder.
In an electronic device, terminals of electronic elements are soldered on a wiring pattern formed on a substrate of a semiconductor chip. Increase in the functions of the device has rendered the terminals to be densely mounted, which requires high accuracy of the soldering operation.
Referring to FIG. 3, a conventional dispenser for applying solder has a syringe 1 in which cream-like solder 2 is charged. The syringe 1 is covered with an air-tight cap 7 having an upper opening. A pressure pipe 8 is attached to the cap 7 for supplying air into the syringe 1 through the opening of the cap.
On the bottom of the syringe 1 is formed a projection 3 having a hole, which engages with a holder 5 of a needle 4. The needle 4 has an axial passage 6 having a diameter about 0.26 mm.
When air pressure is applied to the syringe 1 through the pipe 8, the solder 2 flows downwardly through the holder 5 and the needle 4, and is discharged out from the needle 4. Since the diameter of the passage 6 is small, a strip of solder having an appropriate width is formed.
However, the solder 2 is not always constantly discharged from the needle 4. Moreover, the passage 6 may be clogged with the solder 2. These inconveniences occur under the following circumstances:
(1) The solder 2 contains solids caused by ingredients, such as flux, which are larger than the diameter of the passage 6. PA1 (2) The solder 2 is not homogeneous in viscosity. PA1 (3) The solder 2 is thixotropic so that when the flow rate varies, the viscosity becomes high.